Problem: $\dfrac{3}{10} + \dfrac{15}{100} = {?}$
Explanation: The fractions must have the same denominator before you can add them. Rewrite $\dfrac{3}{10}$ as $\dfrac{30}{100}$ $\dfrac{30}{100} + \dfrac{15}{100} = {?}$ $ = \dfrac{45}{100}$